(1) Field of Invention
(2) Description of Related Art
The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. Nos. 4,539,507, 5,151,629, EP 0676461 and WO 98/27136. The emitting materials employed here, besides fluorescent emitters, are increasingly organometallic complexes which exhibit phosphorescence (M. A. Baldo et al., Appl. Phys. Lett. 1999, 75, 4-6). For quantum-mechanical reasons, an up to four-fold energy and power efficiency is possible using organometallic compounds as phosphorescence emitters. In general, there is still a need for improvement both in the case of OLEDs which exhibit singlet emission and also in the case of OLEDs which exhibit triplet emission, in particular with respect to efficiency, operating voltage and lifetime. This applies, in particular, to OLEDs which emit in the relatively short-wave region, i.e. green and in particular blue.
The properties of OLEDs are determined not only by the emitters employed. In particular, the other materials used, such as host and matrix materials, hole-blocking materials, electron-transport materials, hole-transport materials and electron- or exciton-blocking materials, are also of particular importance here. Improvements in these materials can thus also result in significant improvements in the OLED properties.
According to the prior art, ketones (for example in accordance with WO 2004/093207 or WO 2010/006680) or phosphine oxides (for example in accordance with WO 2005/003253), inter alia, are used as matrix materials for phosphorescent emitters. Further matrix materials in accordance with the prior art are represented by triazines (for example WO 2008/056746, EP 0906947, EP 0908787, EP 0906948).
For fluorescent OLEDs, it is mainly condensed aromatic compounds, in particular anthracene derivatives, that are used in accordance with the prior art as host materials, especially for blue-emitting electroluminescent devices, for example 9,10-bis(2-naphthyl)anthracene (U.S. Pat. No. 5,935,721). WO 03/095445 and CN 1362464 disclose 9,10-bis(1-naphthyl)anthracene derivatives for use in OLEDs. Further anthracene derivatives are disclosed in WO 01/076323, in WO 01/021729, in WO 2004/013073, in WO 2004/018588, in WO 2003/087023 or in WO 2004/018587. Host materials based on aryl-substituted pyrenes and chrysenes are disclosed in WO 2004/016575. Host materials based on benzanthracene derivatives are disclosed in WO 2008/145239. For high-quality applications, it is desirable to have improved host materials available.
However, there is still a need for improvement in the case of the use of these host and matrix materials as also in the case of other host and matrix materials, in particular with respect to the efficiency and lifetime of the device.
Although OLEDs based on small molecules (SMOLEDs) in some cases exhibit fairly good efficiencies, lifetimes and/or operating voltage, thermal vacuum vapour-deposition methods are necessary, which are restricted to a certain device size. For mass production and for larger displays, however, it is desirable to apply the organic materials from solution, for example by means of spin-coating or ink-jet processes, which additionally enable the production costs to be reduced. Light-emitting polymers, oligomers and/or dendrimers are usually used in order to process electroluminescent devices from solution. These compounds often exhibit good solubility in organic aromatic solvents and have good film-formation properties. A further possibility for improving processability consists in incorporating long alkyl chains into a molecule as solubility-promoting groups. Unfortunately, the devices processed from solution using polymers, oligomers and/or dendrimers or molecules having alkyl chains usually have worse performance than comparable small molecules with respect to efficiency, lifetime and operating voltage.